A rod main body and a rod head are generally manufactured by processing a steel material manufactured by continuous casting. Impurities caused by center segregation exist in a central portion of the steel material manufactured by the continuous casting. Therefore, there is a risk that delayed fracture is caused at a center segregation portion if the rod main body and the rod head are joined by friction welding.
JP2011-56531A discloses a piston rod manufacturing method including a step of hollowing out respective axial center portions of a rod main body and a rod head from respective end surfaces thereof to remove impurities caused by center segregation, and a step of joining the respective end surfaces of the rod main body and the rod head by friction welding.
Accordance to the piston rod manufacturing method disclosed in JP2011-56531A, the respective end surfaces of the rod main body and the rod head are joined integrally by friction welding after the impurities existing in the axial center portion have been removed, and thereby, it is possible to manufacture a piston rod having the joining face with no impurities. Therefore, in accordance with the piston rod manufacturing method disclosed in JP2011-56531A, it is possible to improve the joint strength between the rod main body and the rod head.